Research on the variety of seismicity caused by mechanical interaction between fault systems

为了了解日本列岛及其周围地震活动中观测到的远程相关、偏移等复杂现象的原因，我们利用100年大地测量数据导出的断层系统模型进行了断层间相互作用的模拟研究。首先，我们在PC上构建了一个程序，用原始的断层单元数为104的模型进行了模拟，观察到断层之间的相互作用可能导致相邻断层同时破裂和地震活动的迁移。其次，我们将这段代码转移到京都大学数据处理中心的一台超级计算机上，这样我们就可以处理一个有很多故障元素的模型。在每条断层的走向和倾向方向上，我们将原始断层划分为5 × 5个单元。该模型总共有2600个元素。这个模型可以模拟5级这样小的地震。我们还通过改变它们来检查断裂强度变化的影响。上述仿真得到的主要结果如下：(1)整个断层同时破裂的事件很少发生。(2)由于中等规模地震的频率相对较高，模拟的地震活动性不一定符合Guternberg-Richter定律。(3)认识到surua - nankai海槽大地震与日本西南部内陆地震具有互补关系。(4)观测到大事件震源区沿surua - nankai槽的迁移，但其迁移方向在不同时期有所不同。为了验证上述断层系统模型的有效性，我们利用最近的连续GPS数据估计断层运动，并利用新的三边测量数据计算水平应变率。

In order to understand the cause of complex phenomena such as long range correlation, migration etc. that are observed in seismicity in and around the Japanese islands, we conducted a simulation study with a fault system model which was derived from geodetic data for 100 years incorporating interaction between faults.First, we constructed a code on PC, performed a simulation with the original model whose fault elements are 104 and observed that interaction between faults may cause simultaneous rupture on neighboring faults and migration of seismicity.Second, we transferred this code to a supercomputer of the Data Processing Center, Kyoto University, so that we could deal with a model with many fault elements. We divided the original faults into 5 x 5 elements in both the strike and dip directions of each fault. In total, the model has 2600 elements. This model can simulate as small earthquakes as M5. We also examined the effect of variation in rupture strength by changing them. The main results obtained in the above simulation are as follows.(1) Events that simultaneously rupture the entire fault rarely occur.(2) Since the frequencies of medium-size events are relatively high, simulated seismicity does not necessarily fit the Guternberg-Richter's law.(3) A complementary relationship between large earthquakes along the Suruga-Nankai troughs and inland events in southwest Japan is recognized.(4) Migration of source regions of large events along the Suruga-Nankai troughs is observed, but its *rection differs from time to time.Furthermore we estimated fault motions using recent continuous GPS data and calculated horizontal strain rates with new trilateration data in order to examine the validity of the above fault system model.